Aluminum welding fluxes



Patented May 8 1951 ALUMINUM WELDING FLUXES Mike A. Miller and Warren E.Haupin, New Kensington, Pa., assignors to Aluminum Company of America,Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. ApplicationJanuary 15, 1949, Serial No. 71,225

7 Claims.

This invention relates to aluminum welding fluxes, particularly fluxessuitable for coating aluminum arc welding rods. Such fluxes should becapable of forming adherent coatings on aluminum arc welding rods, ifthey are to be applied as coatings; they should have a suitable effectupon the characteristics of the welding arc; and they should produceslags that are readily removed from the work. The fluxes of theinvention are especially effective as coatings on aluminum rods formetallic arc welding of aluminum, but they may also be applied inpowdered form and in welding processes other than arc welding. Becauseof the numerous advantages arising from the use of our fluxes in themetallic arc welding of aluminum, the problems in such applicationsthereof will be first discussed.

Metallic arc welding of aluminum has always been beset by difficulties;the welding rod must be manipulated carefully to obtain smooth depositsof metal and good welds. These difliculties are largely attributable tothe fact that the welding arc is unstable; metal transfer from rod towork tends to take place unevenly and the arc tends to sputter andblow.- By contrast the metallic arc welding of steel has beencomparatively free of these difficulties, the are being relativelystable and the metal transfer smooth. The principal object of theinvention, therefore, is to provide welding fluxes suitable for use inthe metallic arc welding of aluminum and capable of effectivelystabilizing the arc.

Another difficulty in the metallic arc welding of aluminum arises fromthe customary use of rods having flux coatings produced from watercontaining flux mixtures. The moisture in such flux coatings vaporizesand decomposes in the welding process and, consequently, causes the weldmetal to be porous, although it appears to have the favorable effect ofmaking the are a forceful one. To avoid producing porous welds it isnecessary to eliminate moisture from flux coatings, but such eliminationof moisture ordinarily results in a decrease in the arc force,exaggerating the instability of the are. The result is that molten metalaccumulates on the rod and then transfers to the work in large drops orglobules, with shortcircuiting and violent energy surges. Since it isdesirable (and often necessary) to employ dry flux coated rods, it is afurther object of the invention to provide welding fluxes suitable foruse in the metallic arc welding of aluminum and capable of effectivelystabilizing the are even in the absence of moisture. A stable arc isnecessary for satisfactory welding, especially if the are 2' does nothave the force characteristic which is exhibited when there i moisturein the flux.

A general object of the invention is, of course,

to provide multi-purpose aluminum welding fluxes; and a more particularobject is to provide fluxes especially suited to various processes forarc welding aluminum. A further object is to provide aluminum weldingfluxes which may be used to produce adherent coatings on aluminumwelding rods, coatings which are sufficiently flexible so that they willnot readily flake, crack or chip from the rod. A still further andimportant object is to provide aluminum welding fluxes which will notproduce tenacious slags on the work, in whatever form such fluxes areapplied.

We have discovered certain new fluxes that are generally suitable foraluminum welding, and particularly suitable for arc welding aluminum bymethods'employing either bare or coated rods.- They may be employed inpowdered form and supplied directly to the welding zone, or they may beemployed as coatings on aluminum rods. Further, these fluxes adhere wellto aluminum welding rods when employed as coatings thereon; theystabilize the welding are so as to effect soft, quiet, but steadycurrent flow and transfer of molten metal, even in the absence ofmoisture; they do not induce porosity in the weld when employed dry; andthey do not produce difiicultlyremovable slags on the work.

Generally stated our new fluxes have as the vehicle components thereofat least two alkali metal chlorides, and have as the essentialcomplementary components thereof lithium fluoride,

, aluminum fluoride, magnesium fluoride and at least one fluoride fromthe group sodium fluoride and potassium fluoride. They may also containrelatively small amounts of other materials, particularly as hereinafterrecommended. The aforesaid chlorides serve as a vehicle for theaforesaid fluorides and constitute the principal weight of any givenflux, while the aforesaid fluorides serve as essential fluxing agents inan arc stabilizing combination and constitute at least the major part ofthe balance of the weight of the flux.

Of the common alkali metal chlorides, only lithium chloride issignificantly hygroscopic; it is best avoided when dry fluxes aredesired. Of the fluorides mentioned, only potassium fluoride is at allhygroscopic; it also is best avoided when dry fluxes are desired. Sincethe two somewhat hygroscopic materials just mentioned havenonhygroscopic alternates among the other materials mentioned, itfollows that fluxes composed principally, or entirely, ofnon-hygroscopic salts may be made up. Such fluxes are very desirablesince they take up the least moisture and can be readily dried, ifnecessary. Excellent flux coated aluminum welding. rods can be made bymelting and dehydrating a flux made up of non-hygroscopic salts, andthen dipping the aluminum rods in the molten flux bath so that theyacquire dry fused coatings. Thereafter it is possible to store orpackage the fused flux coated rodsin a dry atmosphere, so that evensmall amounts of moisture are not picked up by the flux-coatings.

Further as to the fluorides, it: should be noted that complex fluoridesand appropriate combinations of single fluorides are interchangeable forthe purpose of providing the essential fluorides in our fluxes. fluorideweights will be referred to in specifying the compositions of ourfluxes. For example, cryolite (sodium aluminum fluoride) and mixtures ofsodium fluoride and aluminum fluoride (to the extent they conform to theproportions found in cryolite) are interchangeable in the fluxes.Complex fluorides that may be formed from single fluorides will notusually be specified herein, it being understood that two or morecombinable single fluorides may formv one or more complex fluorides,although the fluoride proportions specified will usually permit of therebein an excess of one or more of the single fluorides. The compositionranges for the fluxes of the invention will now be set forth. Theprincipal weight of any flux should be provided by the alkali metalchlorides, these being the vehicle components of the flux. MoreSpecifically, the total amount of the alkali metal chlorides should beat least 50 per cent by Weight of the entire flux, and less than about85 per cent (preferably 60 to '70 per cent) As with other aluminum we1ding fluxes having an alkali metal chloride vehicle, two or more suchchlorides may be employed, each in individual amounts between about 5and 60 per cent, to provide the total amount required. We prefer toemploy sodium chloride and potassium chloride, which may convenientlyand effectively be present in amounts of about to 40 per cent by weightof sodium chloride (preferably to per cent), and about 25 to per cent ofpotassium chloride (preferably 30 to 40 per cent). It is oftenpreferable to use a slightly greater amount of potassium chloride thansodium chloride; but approximately equal parts of these chlorides areusually satisfactory.

The major portion of the balance of the weight of any flux (over andabove the alkali metal chloride weight) should be provided by thefollowing fluorides: lithium fluoride, aluminum fluoride, magnesiumfluoride and at least one fluoride from the group sodium fluoride andpotassium fluoride, these being the essential complementary componentsof the flux. More specifically, the total amount of these essentialfluorides should be at least about 15 per cent by weight of the entireflux, and less than per cent (preferably 25 to 35 per cent). Further thetotal weight provided by the alkali metal chlorides and the essentialfluorides may equal 100 per cent, to the exclusion of other fluxcomponents, and preferably is at least 90 per cent when other componentsnot significantly deleterious thereto are included, particularly ashereinafter' recommended.

Further, we have discovered that the essential fluorides must be presentin certain critical For convenience, however, single relative amounts inorder to produce welding fluxes which will both stabilize the weldingarc and form easily removable slags. For these purposes, it is firstnecessary that the ratio of the aluminum fluoride to the total magnesiumfluoride and fluoride from. the group sodium fluoride and potassiumfluoride be between about 0.12 to 1 and about 3 to 1 by Weight. Withinthese ratios, it is also necessary that the lithium fluoride be presentin amount between about 10 and 80 partsv per hundred parts by weight ofall of the essential fluorides contained in the flux, thatsaid aluminumfluoride further be present in amount between .about 10 and 67 parts perhundred as aforesaid, that said magnesium fluoride further be present inamount between about minum fluoride, about 10 to 44 parts per hundred asaforesaid; magnesium fluoride, about 5 to 45 parts per hundred asaforesaid; and sodium fluoride, about 5 to 45 parts per hundred asaforesaid, with the ratio of said aluminum fluoride to said sodiumfluoride being between about 0.25 to 1 and about 2.6 to V1 by weight.

In contrast to most prior fluxes for coating aluminum welding rods,which usually contain cryolite, or sodium fluoride and aluminum fluoride in the proportion existing in cryolite, and which sometimescontain lithium fluoride, the fluxes described above each containmagnesium fluoride in addition to sodium fluoride (or notassiumfluoride). Further, the fluxes of the invention always contain asubstantial amount of lithium fluoride. However, a fluoride combi nationconsisting of lithium fluoride and aluminum fluoride alone (or withsodium or potassium fluoride and magnesium fluoride inamounts smallerthan those referred to above) tends to produce a weld slag which issomewhat difficult to remove from the work; but if in accordance withthis invention, appropriate amounts of magnesium fluoride and at leastone fluoride from the group sodium fluoride and potassium fluoride areincluded, this disadvantage is overcome.

The fluxes, as thus far described, have many desirable characteristics,such as a stabilizing effect on the arc, and a fluxing action whichproduc'es easily removable slags. However, further improvements in arcstabilizing and rod adherence properties of these fluxes are obtained,without causing the formation of unduly tenacious slags when the fluxesare used, if sulfur in forms and amounts hereinafter mentioned and anyalkaline earth in forms and amounts hereinafter mentioned are includedin these fluxes. The sulfur content may be supplied in suitablyavailable form from the group consisting of sulfur, the alkali metalsulfides and sulfates, and the alkaline earth sulfides and sulfates; thetotal weight of sulfur supplied should be between about 0.1 and 2 percent. The alkaline earth content may be provided by any of the alkalineearth compounds, particularly the alkaline earth chlorides, fluorides,sulfides or sulfates (the sulfides and sulfates mentioned obviously willsupply the desired sulfur content as well) the total 7 weight ofalkaline earth provided should be between about 0.15 and 5 per cent.

Both the desired sulfur content and the desired alkaline earth contentmay be most conveniently and effectively provided, within the limits foreach as stated above, by incorporating, as a further component in thefluxes described, at least one alkaline earth sulfate in total amountbetween about 0.5 and per cent by weight (preferably 2 to 6 per cent).Strontium sulfate is most effective, but calcium sulfate is also veryeffective and somewhat cheaper.

Instead of employing a single flux of the type described, two or moremixtures of flux components may be employed in juxtaposition as theequivalent thereof, provided the average composition of the mixtures iswithin the composition ranges stated for the invention. For example, twoflux baths may be employed for coating welding rods, the first producingan inner coating which adheres especially well to the rod, and thesecond producing an outer coating making up the necessary overallcomposition of the flux combination. This practice may be desirablesince flux coatings containing substantial amounts of sodium orpotassium fluoride are somewhat fragile and poorly adherent to a rod,although such components are needed to produce easily removable slags.

Specific examples of the fluxes of the invention are given in thefollowing tables and some of their performance characteristics arethereafter mentioned.

Table I.-Typical flux compositions (per cent) Table II .Chlor2'des intypical fluxes s T U v w x Y Totals: (Table I) 67 57 67 59.5 55.5 63.5Ratios: KCl/NaCl. 1+ 1+ 1+ 1.2 1.35 1.22 1.1

Table III .-Fluorides in typical fluxes In addition to the fluxcompositions given in Table I, hundreds of other flux compositions havebeen tested and the examples are to be understood as chosen toillustrate various important aspects of the invention withoutillustrating every composition variation possible. Flux Y is one of themost successful fluxes which we have used. All of the fluxes given asexamples are capable of maintaining an are that is stable, and that hasadequate force. These fluxes may be used as coatings and will adherevery well to the rod, yet the slag produced by these fluxes comes offthe work very cleanly with a slight tapping of the work.

The characteristic capacity of the fluxes of the invention forstabilizing a welding arc can 5 readily be determined quantitativelywhen current (or voltage) records are made by means of a recording meterconnected across the welding circuit. Such records have shown thefollowing comparative results. When typical prior art fluxes were usedto perform a standard welding operation, the welding current variedabout 10 to 15 amperes above and below the mean current value. However,when fluxes of the invention were used, the welding current varied onlyabout 3 to 5 amperes above and below the mean current value. These smallvariations in welding current, obtained when fluxes of the inventionwere employed, are no greater than the moderate variations found toprevail in the metallic arc welding of steel; they indicate that thefluxes of the invention are significantly improved over those previouslyemployed in aluminum welding, since such stable are conditions have notheretofore been obtained in aluminum arc welding.

As was indicated previously an aluminum welding rod may be given a drycoating when dipped one or more times in one or more dehydrated fusedflux baths. The preferred procedure is to preheat the bare aluminum rodto a temperature as high as about 1020 F. before dipping and to maintainthe flux bath or baths at temperatures as high as about 1110 to 1200 R,depending on the melting point of the flux and that of the rod.Likewise, flux slurries may be used to produce rod coatings,particularly if an absolutely dry flux is not necessary. The aluminumwelding rods referred to throughout this specification are, of course,made of aluminum or an aluminum base alloy selected for the welding andother characteristics desired, the word aluminum being generally usedherein to designate aluminum of various grades of purity and alsoaluminum base alloys.

What is claimed is:

1. An aluminum welding flux composed of nonhygroscopic salts, having asthe vehicle components constituting the principal part by weight thereofat least two alkali metal chlorides, and having as the essentialcomplementary component constituting at least the major part of thebalance of the weight thereof lithium fluoride, aluminum fluoride,magnesium fluoride and sodium fluoride, said essential fluorides beingpresent in a total amount of at least about 15 per cent by weight of theentire flux and in relative amounts as follows: the ratio of thealuminum fluoride to the total magnesium fluoride and sodium fluoridebeing between about 0.12 to 1 and about 3 to 1 by weight, the lithiumfluoride being present in amount between about 10 and 80 parts perhundred parts by weight of said essential fluorides, said aluminumfluoride further being present in amount between about 10 and 67 partsper hundred parts by weight of said essential fluorides, said magnesiumfluoride further being present in amount between about 5 and 75 partsper hundred parts by weight of said essential fluorides, and said sodiumfluoride further being present in amount between about 5 and 55 partsper hundred parts by weight of said essential fluorides.

2. An aluminum welding flux according to claim 1 in which said vehiclecomponents are sodium chloride and potassium chloride and the 7. amountof potassium chloride is at least equal to the amount of sodiumchloride.

3. An aluminum welding flux according to claim 1 having as a furthercomponent thereof a total weight of sulfur between about 0.1 and 2 percent made available from the group consisting of sulfur, the alkalimetal sulfides and sulfates, and the alkaline earth sulfides andsulfates, and. containing at least one alkaline earth compound providingin the flux a total alkaline earth weight between about 0.15 and 5 percent.

4. An aluminum welding flux composed of nonhygroscopic salts, having asthe vehicle components constituting the principal part by weight thereofsodium chloride and potassium chloride, and having as the essentialcomplementary components constituting at least the major part of thebalance of the weight thereof lithium fluoride, aluminum fluoride,magnesium fluoride and sodium fluoride, said essential fluorides beingpresent in a total amount of at least about 15 per cent by Weight of theentire flux and in a relative amounts as follows: the ratio of thealuminum fluoride to the total magnesium fluoride and sodium fluoridebeing between about 0.25 to 1 and about 2.6 to 1 by weight, thelithiumfluoridebeing present in amount between about 30 and 55 parts perhundred parts by weight of said essential fluorides, said aluminumfluoride further being present in amount between about and 44 parts perhundred parts by weight of said essential fluorides, said magnesiumfluoride further being present in amount between about 5 and 45 partsper hundred parts by weight of said essenial fluorides, and said sodiumfluoride further being present in amount between about 5 and 45 partsper hundred parts by weight of said essential fluorides.

5. An aluminum welding flux according. to

claim 4 in which the amount of potassium chlo-- ride is at least equalto the amount of sodium chloride.

6. An aluminum welding flux according claim 4 having as a furthercomponent thereof at least one alkaline earth sulfate in total amount 1between about 0.5 and 10 per cent by weight.

7. An aluminum welding flux composed of non- 1 hygroscopic salts,comprising about per cent by weight sodium chloride, about 33.5 per centby weight potassium. chloride, about 14 per cent lithium fluoride, about'7 per cent aluminum fluoride, about 9 per cent magnesium fluoride,about 3 per cent sodium fluoride, and about 3.5 per cent alkaline earthsulfate.

MIKE A. MILLER. WARREN E. I-IAUP-IN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

